The present invention relates generally to seals for liquid pumps and more particularly, to a particular construction and arrangement of elements forming a seal that is primarily adapted for use in fluid pumps such as the so-called water pumps of prime mover engines, including but not limited to engines for automobiles, trucks and construction machinery.
While a wide variety of seals have been developed and/or proposed for use as so-called water pump or fluid pump seals, in most cases the most effective types of seal, considering the need for reliability, economy, and long life, have been so-called mechanical end face seals. In these seals, the so-called primary seal or the seal wherein two components rotate or otherwise move relative to each other is formed where what is termed a seal ring meets what is termed a mating ring, each ring presenting a substantially flat, annular end face in opposition to a counterpart end face on the other element. The portion of these faces, where actual sliding contact is made, is called the seal band. The two units are urged into sealing contact by a resilient means of some sort.
Customarily, the part of the mechanism external to the outer diameter or o.d. portions of the sealing and the mating rings is occupied by the fluid to be sealed. This fluid is normally water or a water/glycol mix in the case of automotive type engines, and water or watery waste in the instance of so-called appliance seals used on washing machines and the like. In addition, the chemical process industry requires similar seals that are the same in principle as the seals just discussed, but sometimes pose the additional requirement of chemical resistance in view of the fluids being handled.
One important requirement for an end face seal is that of providing some relatively constant axial force that, regardless of a variation in the position of the rings, will still urge the sealing rings into mating engagement under operating conditions. If the axial force varies significantly with axial change of ring position, then, where the parts are new or the installed height is relatively low in relation to the specified value, the end face load will be excessive, causing undue temperature rise and rapid wear. If the force drops off abruptly with a change in installed height, the initial loading would be too low if the actual installed height is high; in other words, if the parts are not initially fit tightly enough, they would suffer from an insufficient load and be prone to leakage. If the load varied considerably under conditions of dynamic runout, the proper consistent balance between loads sufficient to maintain the seal and still low enough not to cause wear, could be compromised. Hence, a relatively constant force or that is, a minimal variation in spring force with relative to deflection is preferred. In this manner, a sufficiently high initial force can be applied and that force can be maintained throughout significant dimensional variations without unduly increasing or decreasing the force.
Inasmuch as one component of an end face seal (usually the so-called mating ring), is affixed to a rotary part and the other element, commonly the sealing ring, is fixed relative to a housing or the like, there must be a way of transmitting torque or rotary resistance from the housing to the seal ring. Were the seal ring and the mating ring to turn together, there would be relative motion in an undesired location, causing leakage and failure of the system.
Still further, mechanical end face seals require a secondary or static seal, i.e., a means of ensuring that there is no fluid leakage between components other than those which rotate relative to each other, and this seal must remain effective even if the parts vibrate or move on account of wear or the like.
Another requirement is that the seal ring must be positioned relative to both rotary parts and fixed parts in such a way that the locus of the seal band remains relatively constant.
In the past, the most popular forms of mechanical end face seal have been those wherein a different component is provided for each different function. Normally, a coil spring or the like arranged coaxially with the impeller shaft supplies the axial force, various splines or the like permit axial movement of the parts and provide the ability to transmit torque, and a rubber diaphragm or the like provides the secondary or static seal, and a guide, a bushing or the like centers the seal ring relative to the mating ring.
Besides coaxially arranged coil springs, resilient forces can be provided by other forms of springs. One form of seal, wherein numerous functions are provided in a single part, was described and claimed in U.S. Pat. No. 3,241,843, and in various other patents describing improvements to and variations of such seal. In some instances, a finger type spring has been used or suggested to apply the radial load of the axial load. These applications include those shown in U.S. Pat. No. 2,608,425. Other patents have suggested encasing a metal Belleville washer or the like within rubber. However, in those designs, particularly wherein the rubber/metal member was positioned in a seat formed where radial and axial surfaces met, proper force application could not be reliably insured.
As with all highly engineered products, therefore there has continued to be a need for improved seals, particularly those which may be produced at relatively low costs and which provide superior performance in use. Some of the difficulties which have been created with prior art seals have to do with the manner in which the end face load is applied to the seal. Other difficulties have arisen, particularly wherein the surfaces of rubber parts exposed to the fluid to be sealed are placed in tension either constantly or periodically, initially inducing surface cracking which can ultimately lead to failure of the entire rubber part.
Some seal constructions have had difficulty in the area of precise radial location of the seal ring, especially where significant dynamic eccentricity is present or wherein the members called upon to provide radial location of the ring have been relatively flexible instead of relatively stiff.
Certain other difficulties have arisen with end face seals, particularly fluid pump seals, wherein because of variation in so-called installed heights, there has been an unduly high variation in axial load throughout the life of the seal.
Because of gradual improvements made to engines of various kinds, their service lives have been extended considerably in relation to the service lives of engines produced long ago or even more recently. Thus, while an automotive engine warranty of 12,000 miles was standard in the industry for many years, warranties of 50,000, 60,000 or even 100,000 miles and more are not uncommon, even for less expensive auto engines. Larger, heavier duty engines, such as diesel engines used in over-the-road trucks, have even longer anticipated service lives (such as 500,000 to 1,000,000 miles for example), and accordingly, the water pump seals in such engines should be of a design that would be reasonably expected to provide effective sealing over a period of many years and many thousand hours of actual operation.
An ideal seal is one wherein the applied load varies little or not at all throughout a wide range of installed heights, both those arising from variations in the installed dimensions, thermal expansion, and component wear. By "installed heights" is meant the axial distance between the plane of the end face of the seal ring and a given reference plane, usually the end face surface of a seal-receiving counterbore.
In view of the failure of the prior art to provide an end face seal with improved capabilities for a large variety of applications, it is an object of the present invention to provide an improved end face seal.
Another object of the invention is to provide an end face seal wherein a number of functions required of the seal are provided by a single composite element having two components providing these functions.
Yet another object of the invention is to provide a low-cost seal that will be reliable, and operate for an extended period.
A further object of the invention is to provide an end face seal wherein pressure in the area of the fluid to be sealed augments the sealing action and insures that the elastomeric parts exposed to the seal fluid are not unduly deformed by being subject to tensile stresses.
A still further object of the invention is to provide a seal wherein a novel construction of composite element is provided to insure proper radial location of the seal ring.
An additional object of the invention is to provide a seal wherein a composite element provides the multiple functions of secondary sealing, appropriate establishment and maintenance of axial load and transmission of torque.
Another object of the invention is to provide a liquid pump seal wherein a multi-function composite unit includes a finger or disc type spring element embedded in an elastomeric component that includes a collar adapted to snugly surround a portion of the sealing ring so as to transmit torque or rotary force thereto, to provide a tight secondary seal and to insure proper radial location or alignment of the ring.
Yet another object of the invention is to provide an arrangement of a composite multi-function unit wherein relative motion between this unit and the associated parts will not compromise the effectiveness of the seal or the longevity of the components.
A further object of the invention is to provide a liquid seal which may be readily assembled with a high degree of reliability within a housing, preferably a housing containing a spring retainer element.
A still further object of the invention is to provide a seal having a low-cost composite element that includes a finger or disc spring and two, and in some cases three, annular beads in particularly desired locations, with one of the beads providing several advantages in applying load to the seal ring which may be manufactured reliably at low cost.
An additional objection is to provide a fluid seal wherein a multi-purpose, multi-function composite unit that includes an axially extending collar for engaging and locating a seal ring is also readily adapted for cooperation with a garter spring or other auxiliary radial load-imparting element.
Yet another object is to provide a composite, multi-function unit which, as molded, includes at least two annular formations adapted respectively to apply sealing force to an end of the seal ring and a portion of the housing, which formations will accommodate variations in the radial size of the finger spring as it moves through a range of axial positions.
The foregoing and other objects and advantages of the invention are achieved in practice by providing a novel liquid seal that includes an annular sealing ring having an end face cooperating with a counterpart face on a mating ring to provide an annular, liquid-tight seal band and a multi-function composite member that includes a metal spring unit embedded therein, with the spring having non-linear load/deflection characteristics so that a relatively constant axial load can be applied through a wide range of seal ring movement, at least two molded annular load bearing formations adapted to apply a spring load force to the seal ring from a portion of the housing, and a collar disposed radially intermediate these formations for snugly receiving and radially locating the sealing ring unit.